Circular polarization antenna



May25, 1954 H4, RIBLET v 1 2,679,590

CIRCULAR POLARIZATION ANTENNA Filed Sept. .18, 1945 INVENTOR- HENRY J. RIBLET I ATTORNEY Patented May 25, 1954 CIRCULAR POLARIZATION ANTENNA Henry J. Riblet, Cambridge, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application September 18, 1945, Serial No. 617,154

19 Claims.

My present invention relates to radio antennas in general and in particular to a radio antenna for producing a beam of radio energy having circular polarization.

Although my invention may be used in antennas of various sorts having directivity or not having directivity as may be applicable, it is herein disclosed as embodied in an antenna which is an improvement on the antenna disclosed in my copendingapplication for a Beacon Antenna, Serial No. 600,693, filed June 21, 1945. In my copending application, there are disclosed various embodiments of a pancake beam antenna invented by me. This antenna produces a pancake-shaped beam having polarization in one plane only. It is desirable that such an antenna produce a beam having circular polarization in order to facilitate the reception of transmitted energy by an antenna having any polarization, or located in any locality about the transmitting antenna. Energy polarized in one plane only may be absorbed by obstructions in the air or on the surface of .the earth, and thereby produce blind spots in the region about the antenna. A circularly polarized beam will be less apt to have such blind spots. Further, circularly polarized radiation may be received by a polarized antenna regardless of its orientation.

It is accordingly an object of my invention to provide an antenna having a pancake shaped beam of circularly polarized energy.

It is a further object of my invention to provide such an antenna by properly arranging radiating slots in a transmission line of the wave u d ng type.

It is a still further object of my invention to provide such an antenna which will be simple to construct, and to tune and install.

It is a still further object of my invention to provide such an antenna which will be light in weight, small in size, and inexpensive.

Other and further objects of my invention will become apparent upon a careful consideration of the following detailed description when taken in connection with the drawing, the sole figure of which illustrates an antenna constructed in accordance with my invention.

In the drawing, a hollow cylindrical wave guide I has a first longitudinally disposed linear array of slots 2, 3, 4 and and a second similar array of slots 2, 3', 4' and 5 cut as will be hereinafter described in greater detail in the outer wall 1 thereof. The wave guide I 0 may, if desired, be of the type having an inner conductor. However, the antenna of my invention is constructed solely upon the outer conductor I of the wave guide I0. In the first array, alternate slots 2 and 4 respectively are each disposed longitudinally with respect to the axis of thewave guide l0, while the remaining alternate slots 3 and 5 respectively are each disposed transversely to the said axis. The respective centers of the slots 2, 3, 4 and 5 are spaced apart a distance substantially equal to one-quarter of a wave length of energy in the wave guide I 0. Thus the two longitudinally disposed slots 2 and 4 respectively are one-half such a wave length, or 180 electrical degrees apart, while the two transversely disposed slots 3 and 5, respectively, are also one-half wave length or 180 electrical degrees apart. A transversely disposed slot 3 and a longitudinally disposed slot 2, for example, are or one-quarter wave length apart at their centers. Likewise, the transversely and longitudinally disposed slots 5 and 4 are 90 apart at their centers. A transversely disposed slot 3 or 5 and a longitudinally disposed slot 2 or 4 may be considered to form a pair of mutually perpendicular slots.

Each slot 2, 3, 4 or 5 is provided with a probe 6, 1, '8 or 9, respectively, for the purpose of exciting the slot associated therewith. The probes are each mounted in the wall I of the wave guide It] near a long edge of the therewith associated slot, and extend through the wall I and into the wave guide ID. The effect of a probe 6, I, 8 or 9 upon its associated slot 2, 3, 4 or 5 respectively isto produce electric field vectors in a direction transverse to the line of the associated slot, and therefore, to excite that slot into radiation. The direction of the electric field vector produced across a slot is determined by the position of the associated probe. Thus, if the probe is on one side of the slot, the electric field vector will have one direction, whereas if the probe is on the other side of the slot, this vector will have the opposite direction. Revers ing the position of a probe in this manner is therefore efiective to reverse the phase of excitation of a slot, or change that phase It will be noted that in any pair of mutually perpendicular slots 2 and 3 or 4 and 5 respectively, the electric field vectors H and I2 or 13 and M are substantially mutually perpendicular. It follows that the polarization of the radiation from one slot 2 or 4 of such a pair is substantially perpendicular to the polarization of the radiation from the other slot 3 or 5 of such a pair. In any longitudinally arranged pair of similarly disposed slots the excitation is reversed from one slot to the next. Thus in the two longitudinally disposed slots 2 and 4, for example, the probes 6 and 8 respectively are reversed so that these two slots are excited by the probes substantially 180 out of phase with each other. The second array is substantially identical to the first array. A plurality of such arrays are arranged circumferentially about the wall I of the wave guide l0.

Circularly polarized radiation is produced by the antenna illustrated in the drawing as .follows. Considering a pair of mutually perpendicular slots, as for example, the slots 2 and 3,

it will be recalled that these slots produce radiations which at any one instant are substantially mutually perpendicularly polarized, and that the two slots 2 and 3 are so positioned on the wall I of the wave guide as to be 90 electrical degrees apart. Therefore, these slots are excited substantially 90 out of phase by energy in the wave guide. Hi. It isweli :lmown in the antenna art that two radiating elements which are excited 90 out of phase andwhich produce radiations that are polarized mutually perpendicularly will produce a total radiation having circular polarization. The slots 2 and-3 are such an arrangement of radiating elements, and therefore, their total radiation is circularly polarized.

Pairs of mutually perpendicular slots, such'as slots 2 and 3 or 4 and 5 may be arrayed on a cylindrical wave guide in to produce a pancake beam as illustrated in the drawing. Thus the pair 2 and 3 and the pair 4and 5 are efiectively onehalf wave length apart in the direction of the axis on the wall I of the wave guide [0. As taught in my copending application, hereinabove referred to, this arrangement. will produce a directive beam if the excitingprobes are alternately reversed for adjacent radiators or slots or, as appropriate in this invention for adjacent pairs of slots. Thus, for example, the probes 6 and 8 of the longitudinally arranged slots 2 and 4 respectively are alternated in position about their respective slots. This provides for a 180 phase shift in the feed of these two slots 2 and 4. However, since these slots are already 180 electrical degrees apart on the wall I of the wave guide I0, the total phase shift is. 360 and these twoslots are excited in phase with each other.

Similar reasoning willreveal. that the two transversely disposed slots 3 and 5 are also excited in phase with each other. Thus the longitudinally disposed slots-2 and4 are all excited in phase with each other, and the transversely disposed slots 3 and 5 are likewise. all. excited in phase with each other, but the phase of thelongitue dinally disposed slot. is 90 difierent from the phase of the transversely disposed slot. This 90 difierence results. in. circular polarization of the radiation produced by the. arrays of slots, as hereinabove-set forth. The fact that similarly disposed slots are excited inphase with each other results in a directive beam from each array of slots. Directivity will be in a direction at right angles to the line of the array. The further arrangement of similar arrays of slots about the wall I to form circumferential arrays of similarly disposed and excited slots will result in a relatively pancake shaped beam having directivity in any plane containing the axis of .the wave guide l0 and in a direction substantiallyperpendicular .to the said axis but, having relatively no directivity about saidaxisin .the planev per.- pendicular thereto.

It will be apparent that, from another aspect,

- ing,,a hollow cylindrical. wave guide, .a

my invention may be described as a radio antenna comprising, on the wall of the wave guide ill, a plurality of circumferential arrays of alternately solely longitudinally and solely transversely disposed slots 2, 3, 4, and 5, adjacent arrays being spaced substantially apart. All the longitudinal slots are excitedin one first phase,. while all the transverse slots are excited in a second phase which is 90 different from the first phase. The radiations produced by the individual longitudinal slots are polarized substantially perpendicular to the radiations produced by the individual transverse slots.

Althoughl have shown and described an arrangement of antenna slots in accordance with my invention in an antenna of a type used for producing a pancake beam, it is to be understood that my invention may be used in any form of radio antenna or array. Therefore, my invention is not to be limited except as required by .the extent of the prior art and the spirit of the appended claims.

I claim:

1. Apparatus for producing a pancake shaped beam of circularly polarized radiation comprising, a transmission line having a cylindrical outer wall andaplurality of pairs of substantially mutually perpendicularly disposed first and second slots in said wall, said first andsecond slots being adapted forv the.radiationtherethrough of substantially mutually perpendicularly polarized waves and being spacedapart longitudinally with respect to said line a distance substantially equal to one quarter the wave. length. of energy insaid line, groups of said pairs being arrangedinat least two adjacent. circumferential arrays about said wall, adjacent arrays being spaced apart a distance substantially equal to one half of said wave length, said first. slotsbeing all excited in the same first phase and said second slots being all excited in a secondphase substantially ninety degrees different. from said first phase.

Apparatus for producinga pancake shaped beam of circularly polarized radiation comprisplurality of first andsecond slots therein and aplurality of probes for exciting said slots mounted in and extending into said wave guide one near a long edge of. each of ,saidslots, said jfirst slot being disposed. longitudinally 1 of said wave guide and said second slots being disposed 'transverselyof said wave guide, said slots being disposed about said wave guide in a plurality ofv circumferential arrays comprising solely first or second slots alternately, said arrays being spaced apart longitudinally of. said Wave guide adistance substantially. equal at their respective centers to one quarter wave length of energy in said wave guide, the probes of successive arrays Of first slotsbeing on opposite sides of their respective slots and the probes of successive arrays of .second slots being on opposite .sides oftheir respectiveslots, said first and second slots bein excited to produce substantially mutually perpendicularly polarized radiation, said. first slots being excited in the same first phase, and said second slots:being excitedin a second phasesubstantially ninety degrees different from said first phase.

3. A radio antenna comprising, a hollow ,cylindrical wave guide havingaplurality .of transversely disposed slots in the wall thereof and a pluralityof probes in said wall one nearthe center of a long edge. of eachof said slots, said slots being arrayed circumferentially of said wall in longitudinally spaced groups substantially one half wave length of energy in said wave guide apart, said probes in adjacent groups being oppositely located with respect to their respective slots.

4. An antenna comprising a transmission line having an outer wall formed with a first slot and a second slot, said first slot bein disposed in nonparallel relationship with said second slot.

5. An antenna comprisin a transmission line having an outer wall formed with first and second longitudinally spaced slots, said first slot being disposed in nonparallel relationship with said second slot.

6. An antenna comprisin a transmission line having an outer wall formed with a first slot and a second slot, said slots being spaced apart longitudinally of said transmission line, said first slot being disposed in nonparallel relationship with said second slot, and means for exciting said slots.

7. An antenna comprising a transmission line havin an outer Wall formed with a plurality of circumferentially arrayed pairs of slots, each of said pairs of slots comprising a first slot and a second slot, said first and second slots being spaced apart longitudinally of said transmission line, said first slot being disposed in nonparallel relationship with said second slot, and means for exciting said slots.

8. An antenna comprising a transmission line having an outer wall formed with a plurality of longitudinally arrayed pairs of slots, each of said pairs of slots comprisin a first slot and a second slot, said first and second slots being spaced apart longitudinally of said transmission line, said first slot being disposed in nonparallel relationship with said second slot.

9. Apparatus as in claim 8 and means for exciting said slots.

10. An antenna comprising a transmission line having an outer wall formed with first and second mutually perpendicular slots.

11. An antenna comprising a transmission line having an outer wall formed with mutually perpendicular slots spaced longitudinally of said transmission line.

12. Apparatus for producing nonlinearly polarized radiation comprisin a cylindrical transmission line having an outer wall formed with first and second mutually perpendicular slots spaced longitudinally of said transmission line, and means for exciting said slots.

13. Apparatus as in claim 12 wherein said lastmentioned means is a probe for each of said slots mounted in said wall near one long edge of each of said slots, said probes extending into said transmission line.

14. An antenna comprising a wave guide having an outer wall formed with a plurality of cir- 6 cumferentially arrayed pairs of slots, each of said pairs comprising first and second mutually perpendicular slots spaced longitudinally of said transmission line.

15. An antenna comprising a wave guide formed with at least two longitudinally arrayed pairs of slots, each of said pairs of slots compris ing first and second slots spaced longitudinally of said transmission line, the first slot of one pair being parallel to the first slots of the other pairs.

16. Apparatus as in claim 15 and means for exciting said slots.

17. Apparatus as in claim 15 and means for exciting said slots in phase quadrature with respect to each other.

18. Apparatus for producing circularly polarized radiation comprising a cylindrical transmission line having an outer wall formed with a first slot and second slot, said slots being spaced apart longitudinally of said transmission line substantially one-quarter wave length of the energy in said transmission line, said first slot being disposed transversely of said line, said second slot being disposed longitudinally of said line, and means for exciting said slots in phase quadrature with respect to each other.

19. Apparatus for producing circularly polarized radiation comprising a cylindrical transmission line having an outer wall formed with a plurality of circumferentially arrayed pairs of slots, each of said pairs comprising a first slot and a second slot, said first and second slots being spaced apart longitudinally of said transmission line substantially one-quarter wave length of the energy in said transmission line, said first slot being disposed transversely of said line, said second slot being disposed longitudinally of said line, and means for exciting said slots in phase quadrature with respect to each other.

References Cited in the file ofthis patent UNITED STATES PATENTS Number Name Date 2,405,242 Southworth Aug. 6, 1946 2,408,435 Mason Oct. 1, 1946 2,412,320 Carter Dec. 10, 1946 2,414,266 Lindenblad Jan. 14, 1947 2,433,368 Johnson Dec. 30, 1947 2,461,005 Southworth Feb. 8, 1949 2,464,276 Varian Mar. 15, 1949 2,473,274 Bradley June 14, 1949 2,477,510 Chu July 26, 1949 2,480,208 Alvarez Aug. 30, 1949 2,488,419 Lindenblad Nov. 15, 1949 2,507,528 Kandoian May 16, 1950 FOREIGN PATENTS Number Country Date 493,695 Great Britain Oct. 13, 1938 

